Positive photoresist composition and method of patterning resist thin film for use in inclined implantation process

ABSTRACT

A composition includes (A) a novolak resin containing at least 20% by mole of a m-cresol repeating unit and having a 1-ethoxyethyl group substituting for part of hydrogen atoms of phenolic hydroxyl groups, (B) a quinonediazide ester of, for example, the following formula, and (C) 1,1-bis(4-hydroxyphenyl)cyclohexane.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a positive photoresistcomposition and a method of patterning a resist thin film for use in aninclined implantation process. More specifically, it relates to a highlysensitive positive photoresist composition that is used inphotolithography using i-line (365 nm) and specifically advantageouslyin an inclined implantation process using a very thin resist film about0.1 to 0.5 μm thick, as well as to a method of patterning a resist thinfilm for use in the inclined implantation process using the positivephotoresist composition.

[0003] 2. Description of the Related Art

[0004] Photoresist compositions each containing an alkali-soluble resinand a quinonediazido-group-containing compound have satisfactorydefinition, sensitivity, etching resistance and thermal resistance in aphotolithography process using i-line (365 nm) and therefore have beenapplied to practical use in fabrication of semiconductor devices andliquid crystal devices.

[0005] Such resist patterns having a size smaller than the wavelength ofexposing light have been believed to be hardly formed byphotolithography without deteriorating the above properties. However,fine resist patterns of about 0.35 μm, smaller than the wavelength ofi-line, can now be formed as a result of improvements in materials,process conditions and exposure techniques.

[0006] With increasing diameters of silicon substrates forsemiconductors and glass substrates for liquid crystal display devices,increasing demands have been made on positive photoresist compositionswith higher sensitivity to improve throughputs. Improvements inconventional positive photoresist compositions each containing analkali-soluble resin and a quinonediazido-group-containing compound havetherefore been proposed.

[0007] For example, Japanese Patent Laid-Open No. 3-249654 discloses aphotosensitive composition containing a polymeric compound (e.g., anovolak resin) having an acid-decomposable substituent, and a1,2-naphthoquinonediazido-4-sulfonic acid ester.

[0008] However, the photosensitive composition often invites insolublematters to form during storage and must have higher definition andsensitivity. In addition, the photosensitive composition is readilydeactivated upon contact with a basic substance in the air to vary itssensitivity and is thereby insufficient in post-coating delay (PCD; timeinterval between coating process and exposure process) stability andpost-exposure delay (PED; time interval between exposure process topost-exposure baking (PEB) process) stability. In short, the resistcomposition is insufficient in “stability of latent image beforedevelopment.”

[0009] Japanese Patent Laid-Open No. 5-127386 discloses a photosensitivecomposition containing a polymer and a photosensitive acid generator(e.g., an orthoquinonediazidosulfonic acid ester), which polymercomprises a hydrogenated alkali-soluble resin (e.g., a novolak resin)having a phenol skeleton and having dissolution inhibiting groups beingunstable to acids and being combined with its phenolic hydroxyl groups.

[0010] However, the photosensitive composition must be exposed toexcimer laser light and thus invites high production cost.

[0011] Japanese Patent Laid-Open No. 5-181279 discloses a photosensitivecomposition containing a polyhydroxystyrene polymer having anacid-decomposable substituent, and a photosensitive acid generator(e.g., an orthoquinonediazidosulfonic acid ester).

[0012] The photosensitive composition, however, often invites insolublematters to form during storage and must have higher sensitivity anddefinition.

[0013] Japanese Patent Laid-Open No. 6-130665 discloses a photosensitivecomposition containing an alkali-soluble resin (e.g., a novolak resin)having an acid-decomposable substituent, and a photosensitive acidgenerator (e.g., a quinonediazide compound).

[0014] The photosensitive composition, however, must be exposed toexcimer laser light and thus invites high production cost.

[0015] Japanese Patent Laid-Open No. 6-202320 discloses a photosensitivecomposition containing an alkali-soluble resin (e.g., a novolak resin)having an acid-decomposable substituent, and a1,2-naphthoquinonediazido-4-sulfonic acid ester of apolyhydroxybenzophenone.

[0016] The photosensitive composition, however, often invites insolublematters to form during storage and must have higher sensitivity anddefinition.

[0017] Japanese Patent Laid-Open No. 7-5682 discloses a resistcomposition containing a polyhydroxystyrene polymer having anacid-decomposable substituent, and a 1,2-naphthoquinonediazide compound.

[0018] However, the resist composition must be exposed to excimer laserlight and thus invites high production cost.

[0019] Japanese Patent Laid-Open No. 9-179300 discloses a resistcomposition containing a polyhydroxystyrene polymer having anacid-decomposable substituent, a photosensitive acid generator (e.g., aquinonediazide compound), and an acid-diffusion controlling agent.

[0020] However, the resist composition must be exposed to excimer laserlight and thus invites high production cost.

[0021] In addition, all the aforementioned compositions must be improvedin their stability of latent image before development.

[0022] Separately, an “inclined implantation” process is proposed in,for example, Japanese Patent Laid-Open No. 8-22965. In this process, aninclined semiconductor substrate having a patterned resist mask issubjected to ion implantation to thereby selectively implant dopant ionsto a surface of the semiconductor substrate.

[0023] The process is believed to be effective for selective ionimplantation into a small area of the substrate directly below thepatterned resist or into side walls of holes disposed on the substrate.

[0024] When an ultrafine resist pattern of about 0.35 μm is formed bythe inclined implantation process, a patterned resist film serving as amask must be very thin of about 0.1 to 0.5 μm so as not to inhibit ionimplantation.

[0025] However, when very thin resist films are formed usingconventional positive photoresist compositions, the resulting very thinresist films cannot yield satisfactory latent images, are reduced inthickness in unexposed portions, invite large amounts of scum, or cannotyield patterned resists having a good shape.

[0026] In addition, the patterned resist films are exposed to elevatedtemperatures during implantation process and must have high thermalresistance. Accordingly, the resist films are subjected to “post-baking”heat treatment after development. The positive photoresist compositionsfor use in the implantation process must have sufficient thermalresistance to resist deformation of patterned resist films duringpost-baking.

[0027] Positive photoresist compositions for use in the inclinedimplantation process using a patterned resist thin film about 0.1 to 0.5μm thick must yield a patterned resist film with high definition andcontrast and satisfactory shape, must have high sensitivity, invite lessscum and have satisfactory stability of latent image before developmentand high thermal resistance.

SUMMARY OF THE INVENTION

[0028] Accordingly, an object of the present invention is to provide apositive photoresist composition that has highly improved sensitivityand definition, can yield a patterned resist thin film with highcontrast, invites less scum and has satisfactory stability of latentimage before development and thermal resistance specifically in aninclined implantation process.

[0029] Another object of the present invention is to provide a method ofpatterning a resist thin film for use in an inclined implantationprocess using the positive photoresist composition.

[0030] After intensive investigations, the present inventors have solvedthe problems of the conventional technologies.

[0031] Specifically, the present invention provides, in an aspect, apositive photoresist composition including:

[0032] (A) a novolak resin containing equal to or more than 20% by moleof a m-cresol constitutional repeating unit in total phenolicconstitutional repeating units and having 1-ethoxyethyl groupssubstituting for part of hydrogen atoms of phenolic hydroxyl groups;

[0033] (B) a quinonediazide ester represented by following Formula (I):

[0034] wherein each of R¹, R², R³, R⁴, R⁵, R⁶, R⁷, and R⁸ isindependently a hydrogen atom, a halogen atom, an alkyl group containing1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, ora cycloalkyl group;

[0035] each of R⁹, R¹⁰, and R¹¹ is independently a hydrogen atom or analkyl group containing 1 to 6 carbon atoms;

[0036] Q is a hydrogen atom or an alkyl group containing 1 to 6 carbonatoms, or Q is combined with R⁹ to form a cycloalkyl group containing 3to 6 carbon members or a residue represented by following Formula (II):

[0037] wherein each of R¹² and R¹³ is independently a hydrogen atom, ahalogen atom, an alkyl group containing 1 to 6 carbon atoms, an alkoxygroup containing 1 to 6 carbon atoms, or a cycloalkyl group; and

[0038] c is an integer of from 1 to 3;

[0039] each of Ds is independently a hydrogen atom or a1,2-naphthoquinonediazido-5-sulfonyl group, where at least one of Ds isa 1,2-naphthoquinonediazido-5-sulfonyl group;

[0040] each of a and b is independently an integer of from 1 to 3;

[0041] d is an integer of from 0 to 3; and

[0042] n is an integer of from 0 to 3; and

[0043] (C) a phenolic compound represented by following Formula (III):

[0044] wherein each of R¹, R², R³, R⁴, R⁵, R⁶, R⁷, and R⁸ isindependently a hydrogen atom, a halogen atom, an alkyl group containing1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, ora cycloalkyl group;

[0045] each of R⁹, R¹⁰, and R¹¹ is independently a hydrogen atom or analkyl group containing 1 to 6 carbon atoms;

[0046] Q is a hydrogen atom or an alkyl group containing 1 to 6 carbonatoms, or Q is combined with R⁹ to form a cycloalkyl group containing 3to 6 carbon members or a residue represented by following Formula (IV):

[0047] wherein each of R¹² and R¹³ is independently a hydrogen atom, ahalogen atom, an alkyl group containing 1 to 6 carbon atoms, an alkoxygroup containing 1 to 6 carbon atoms, or a cycloalkyl group; and

[0048] c is an integer of from 1 to 3;

[0049] each of a and b is independently an integer of from 1 to 3;

[0050] d is an integer of from 0 to 3; and

[0051] n is an integer of from 0 to 3.

[0052] The positive photoresist composition may further include (D) atleast one compound capable of absorbing light with a wavelength ofapproximately 365 nm.

[0053] Preferably, the positive photoresist composition further includes(E) at least one amine.

[0054] The positive photoresist composition may further include (F) atleast one organic carboxylic acid.

[0055] Preferably, the 1-ethoxyethyl group substitutes for 30% to 70% bymole of hydrogen atoms of phenolic hydroxyl groups in the novolak resin(A).

[0056] A resist film prepared from the positive photoresist compositionpreferably has a B parameter of from 0.2 to 1.0.

[0057] The positive photoresist composition of the present invention hashighly improved sensitivity and definition, can yield a patterned resistthin film with high contrast, invites less scum, has satisfactorythermal resistance and stability of latent image before development andthereby can be advantageously used in an inclined implantation process.

[0058] The present invention provides, in another aspect, a method ofpatterning a resist thin film for use in an inclined implantationprocess. The method includes the steps of:

[0059] (1) applying a solution of the positive photoresist compositionto a substrate and drying the applied solution to thereby form a resistfilm having a thickness of from 0.1 to 0.5 μm;

[0060] (2) selectively exposing the resist film through a mask;

[0061] (3) subjecting the exposed resist film to post-exposure baking;

[0062] (4) developing the resulting resist film with an aqueous alkalinesolution to thereby dissolve and remove exposed portions of the resistfilm; and

[0063] (5) post-baking the resulting film.

[0064] By using the positive photoresist composition of the presentinvention, the method can pattern a resist thin film that can beadvantageously used in an inclined implantation process.

DETAILED DESCRIPTION OF THE INVENTION

[0065] Novolak Resins (A)

[0066] Novolak resins for use as the ingredient (A) in positivephotoresist compositions of the present invention can be novolak resinseach having equal to or more than 20% by mole of a m-cresolconstitutional repeating unit in total phenolic constitutional repeatingunits and having a 1-ethoxyethyl group substituting part of hydrogenatoms of phenolic hydroxyl groups.

[0067] The term “m-cresol constitutional repeating unit” used hereinmeans and includes constitutional repeating units derived from m-cresolused as a phenol in the preparation of the novolak resins (A) and is forexample represented by the following formulae.

[0068] The term “phenolic constitutional repeating units” means andincludes constitutional repeating units derived from phenols used in thepreparation of the novolak resins (A).

[0069] The novolak resins (A) can be prepared by any process. Forexample, they can be prepared by preparing an unprotected novolak resinin the following manner and replacing part of hydrogen atoms of itsphenolic hydroxyl groups with 1-ethoxyethyl group. Such unprotectednovolak resins can be prepared by dissolving phenols containing equal toor more than 20% by mole of a m-cresol constitutional repeating unit, analdehyde or ketone in an organic solvent, and subjecting the componentsto polycondensation in the presence of an acidic catalyst.

[0070] The content of the m-cresol constitutional repeating units in thetotal phenolic constitutional repeating units of the ingredient (A) ispreferably equal to or more than 20% by mole, more preferably equal toor more than 60% by mole, and most preferably 100% by mole, i.e., them-cresol constitutional repeating units occupy 100% of the totalphenolic constitutional repeating units. If the content of the m-cresolconstitutional repeating units is less than 20% by mole, the resultingpositive photoresist composition may fail to have well-balancedmolecular weight, molecular weight distribution and dissolving rate inalkaline solutions and may fail to yield a patterned resist film with agood shape.

[0071] Phenols that can be used in the preparation of the ingredient (A)in addition to m-cresol include, but are not limited to, phenol;p-cresol, o-cresol; 2,3-xylenol, 2,5-xylenol, 3,5-xylenol, 3,4-xylenol,and other xylenols; m-ethylphenol, p-ethylphenol, o-ethylphenol,2,3,5-trimethylphenol, 2,3,5-triethylphenol, 4-tert-butylphenol,3-tert-butylphenol, 2-tert-butylphenol, 2-tert-butyl-4-methylphenol,2-tert-butyl-5-methylphenol, and other alkyl-substituted phenols;p-methoxyphenol, m-methoxyphenol, p-ethoxyphenol, m-ethoxyphenol,p-propoxyphenol, m-propoxyphenol, and other alkoxy-substituted phenols;o-isopropenylphenol, p-isopropenylphenol, 2-methyl-4-isopropenylphenol,2-ethyl-4-isopropenylphenol, and other isopropenyl-substituted phenols;phenylphenol, and other aryl-substituted phenols;4,4′-dihydroxybiphenyl, bisphenol A, resorcinol, hydroquinone,pyrogallol, and other polyhydroxyphenols. Each of these phenols can beused alone or in combination.

[0072] Aldehydes for use in the preparation of the ingredient (A)include, but are not limited to, formaldehyde, paraformaldehyde,trioxane, acetaldehyde, propionaldehyde, butyraldehyde,trimethylacetaldehyde, acrolein (acrylaldehyde), crotonaldehyde,cyclohexanecarbaldehyde, furfural, furylacrolein, benzaldehyde,terephthalaldehyde, phenylacetaldehyde, α-phenylpropylaldehyde,β-phenylpropylaldehyde, o-hydroxybenzaldehyde, m-hydroxybenzaldehyde,p-hydroxybenzaldehyde, o-methylbenzaldehyde, m-methylbenzaldehyde,p-methylbenzaldehyde, o-chlorobenzaldehyde, m-chlorobenzaldehyde,p-chlorobenzaldehyde, and cinnamaldehyde. Each of these aldehydes can beused alone or in combination. Among these aldehydes, formaldehyde ispreferred for its high availability. To improve thermal resistance ofthe positive photoresist composition, a combination use of ahydroxybenzaldehyde and formaldehyde is typically preferred.

[0073] Ketones for use in the preparation of the ingredient (A) include,but are not limited to, acetone, methyl ethyl ketone, diethyl ketone,and diphenyl ketone. Each of these ketones can be used alone or incombination. An appropriate combination use of an aldehyde with a ketoneis also acceptable.

[0074] The amount of the aldehyde(s) and/or ketone(s) is preferably fromabout 40% to about 85% by weight relative to the phenols.

[0075] Acidic catalysts for use in the preparation of the ingredient (A)include, but are not limited to, hydrochloric acid, sulfuric acid,formic acid, oxalic acid, and p-toluenesulfonic acid. The amount of theacidic catalyst is preferably from about 0.05% to about 5% by weightrelative to the phenols.

[0076] Organic solvents for use in the preparation of the ingredient (A)include, but are not limited to, methanol, ethanol, propanol, butanol,ethylene glycol, propylene glycol, and other alcohols; diethylene glycoldimethyl ether, propylene glycol monopropyl ether, 1,2-dimethoxyethane,1,2-diethoxyethane, and other ethers; tetrahydrofuran, 1,4-dioxane, andother cyclic ethers; acetone, methyl ethyl ketone, methyl isobutylketone, methyl amyl ketone, and other ketones; γ-butyrolactone and othercyclic esters. The amount of the organic solvent(s) is preferably fromabout 100% to about 200% by weight relative to the phenols forsatisfactory cost and reaction rate.

[0077] The novolak resins prepared above are novolak resins beforesubstitution of part of hydrogen atoms of phenolic hydroxyl groups with1-ethoxyethyl groups (hereinafter briefly referred to as “unprotectednovolak resin(s)”). The unprotected novolak resins have a weight averagemolecular weight (Mw) in terms of polystyrene of preferably from about1500 to about 10000, and more preferably from about 2000 to about 5000.

[0078] Preferably, low molecular weight fractions of the unprotectednovolak resins are removed by, for example, fractionation. Techniquesfor the removal are not specifically limited, but such low molecularweight fractions are preferably removed in the following manner. Asolution of the alkali-soluble resin is dissolved in methyl amyl ketone(MAK), and the resulting solution is washed with water to remove acatalyst and unreacted materials. To the residual is added a poorsolvent such as hexane or heptane, or a hexane-MAK or heptane-MAKmixture, and the resultant mixture is stirred and then allowed to standto separate a poor solvent layer containing high molecular weightfractions as a lower layer, and an MAK layer containing low molecularweight fractions as an upper layer. The lower layer is extracted andthereby yields an unprotected novolak resin having a higher molecularweight.

[0079] If the weight average molecular weight Mw of the unprotectednovolak resin is less than about 1500, the resulting composition may notbe applied in a satisfactory manner. In contrast, if it exceeds about10000, the resulting composition may have deteriorated definition. Themolecular weight distribution [(weight average molecular weight)/(numberaverage molecular weight)=Mw/Mn] of the unprotected novolak resin ispreferably less than or equal to 6 and more preferably less than orequal to 4 to yield a patterned resist film having a good shape.

[0080] In addition, the unprotected novolak resin preferably has highersolubility in an alkaline aqueous solution (a developer solution). Aresist film 1 μm thick prepared from the unprotected novolak resincompletely dissolves in 2.38% by weight tetramethylammonium hydroxide(TMAH) aqueous solution at 23° C. preferably within ten seconds and morepreferably within five seconds. In the above procedure, the resist filmis prepared by dissolving the unprotected novolak resin in anappropriate solvent such as 2-heptanone, applying the solution to asubstrate to yield a film, and drying the film at 110° C. for 90seconds.

[0081] By using such an unprotected novolak resin having very highsolubility in an alkaline aqueous solution (developer solution), theresulting positive photoresist composition has satisfactory thermalresistance and stability of latent image before development, has highlyimproved sensitivity and definition and can yield a patterned resistthin film with high contrast that is suitable for use in the inclinedimplantation process.

[0082] The novolak resin (A) for use in the positive photoresistcompositions of the present invention can be prepared by substituting orreplacing part of hydrogen atoms of phenolic hydroxyl groups in theunprotected novolak resins with a 1-ethoxyethyl group. By using thenovolak resin (A) having the 1-ethoxyethyl group, unexposed portions ofthe resulting resist film have increased insolubility and, in contrast,exposed portions thereof have increased solubility in an alkalineaqueous solution (developer solution) to thereby yield a patternedresist film with high contrast.

[0083] The process for substituting part of hydrogen atoms of phenolichydroxyl groups of the unprotected novolak resin with a 1-ethoxyethylgroup is not specifically limited and includes the following process.Initially, the unprotected novolak resin is dissolved in an organicsolvent, the resulting solution is treated with an acid and a compoundcorresponding to 1-ethoxyethyl group, such as 1-ethoxyethene, at atemperature from about 20° C. to about 70° C. for about 1 to about 10hours. The reaction mixture is then neutralized with a basic substance(basic catalyst), is treated with, for example, an ion exchange resin toremove the basic catalyst, salts and other unnecessary components in thereaction mixture, is concentrated using an evaporator to remove theorganic solvent under reduced pressure and thereby yields the novolakresin as the ingredient (A) having 1-ethoxyethyl groups substituting forpart of hydrogen atoms of phenolic hydroxyl groups.

[0084] Such organic solvents for use herein are not specificallylimited, as long as they can dissolve the ingredient (A), and can bechosen from those used in the preparation of the unprotected novolakresins. Preferred organic solvents are those that are not miscible withan acid aqueous solution or water used in a washing process after thereaction, of which 1,4-dioxane is typically preferred.

[0085] The basic catalyst includes, but is not limited to, ethylamine,ethanolamine, diethylamine, diisopropylamine, diethanolamine,dicyclohexylamine, and other primary and secondary amines;trimethylamine, triethylamine, tripropylamine, and other tertiary amineseach containing a lower alkyl group, of which triethylamine ispreferred.

[0086] The acid includes, for example, p-toluenesulfonic acid.

[0087] The 1-ethoxyethyl group is an acid-decomposable group that can bedecomposed by action of an acid. Such acid-decomposable groups furtherinclude methoxymethyl group, 1-methoxyethyl group, tert-butyl group,trimethylsilyl group, and tert-butoxycarbonyl (t-BOC) group. Among theseacid-decomposable groups, 1-ethoxyethyl group can be most efficientlydecomposed by action of an acid derived from the quinonediazide ester(B) used in the present invention.

[0088] In the ingredient (A), the 1-ethoxyethyl group substitutes forpreferably about 30% to about 70% by mole, and more preferably about 40%to about 60% by mole of hydrogen atoms of phenolic hydroxyl groups. Ifthis rate is less than 30% by mole, the positive photoresist compositionmay have insufficient contrast in development and may invite increasedscum. In contrast, if it exceeds 70% by mole, the positive photoresistcomposition may have deteriorated sensitivity and definition, may failto yield finely patterned resist films, or may yield patterned resistfilms with a T-top profile.

[0089] The novolak resin (A) having 1-ethoxyethyl group preferably haslower solubility in an alkaline aqueous solution to yield patternedresist films with high contrast. For example, it preferably takes for aresist film 1 μm thick prepared from the novolak resin (A) to completelydissolve in 5.0% by weight tetramethylammonium hydroxide (TMAH) aqueoussolution equal to or more than 300 seconds. In this procedure, theresist film is prepared by dissolving the novolak resin (A) in anappropriate solvent, such as 2-heptanone, to yield a solution, applyingthe solution to a substrate to yield a film, and drying the film at 110°C. for 90 seconds.

[0090] An example is shown below in which a 1-ethoxyethyl groupsubstitutes for a hydrogen atom of a phenolic hydroxyl group.

[0091] Quinonediazide Esters (B)

[0092] Quinonediazide esters for use as the ingredient (B) in thepositive photoresist compositions of the present invention can bequinonediazide esters each having at least one1,2-naphthoquinonediazido-5-sulfonyl group in its molecule andrepresented by Formula (I).

[0093] The quinonediazide esters (B) can be prepared by subjecting acompound of Formula (I), wherein all Ds are hydrogen atoms, tocondensation with a 1,2-naphthoquinonediazido-5-sulfonyl halide andesterifying the condensation product partially or completely. Thecondensation is advantageously performed in an organic solvent such asdioxane, N-methylpyrrolidone and dimethylacetamide in the presence of abasic condensing agent such as triethylamine, alkali metal carbonatesand alkali metal hydrogencarbonates. In this procedure, preferably equalto or more than 50% by mole, and more preferably equal to or more than60% by mole of total hydroxyl groups in the phenolic compound isesterified with the 1,2-naphthoquinonediazido-5-sulfonyl halide. Inother words, the quinonediazide esters (B) for use herein preferablyhave an esterification percentage of equal to or more than 50% and morepreferably equal to or more than 60%. Such quinonediazide esters canhave higher definition.

[0094] By using the ingredient (B), the positive photoresistcompositions of the present invention have satisfactory sensitivity anddefinition and can achieve definition of 0.35 μm or below inphotolithography using i-line.

[0095] Preferred examples of the quinonediazide esters (B) representedby Formula (I) are quinonediazide esters of:

[0096] 2,4-bis(3,5-dimethyl-4-hydroxybenzyl)-5-hydroxyphenol,2,6-bis(2,5-dimethyl-4-hydroxybenzyl)-4-methylphenol, and other lineartrinuclear compounds;

[0097]bis[2,5-dimethyl-3-(2-hydroxy-5-methylbenzyl)-4-hydroxyphenyl]methane,bis[2,5-dimethyl-3-(4-hydroxy-5-methylbenzyl)-4-hydroxyphenyl]methane,bis[2,5-dimethyl-3-(4-hydroxybenzyl)-4-hydroxyphenyl]methane,bis[3-(3,5-dimethyl-4-hydroxybenzyl)-4-hydroxy-5-methylphenyl]methane,bis[3-(3,5-dimethyl-4-hydroxybenzyl)-4-hydroxy-5-ethylphenyl]methane,bis[3-(3,5-diethyl-4-hydroxybenzyl)-4-hydroxy-5-methylphenyl]methane,bis[3-(3,5-diethyl-4-hydroxybenzyl)-4-hydroxy-5-ethylphenyl]methane,bis[2-hydroxy-3-(3,5-dimethyl-4-hydroxybenzyl)-5-methylphenyl]methane,bis[2-hydroxy-3-(2-hydroxy-5-methylbenzyl)-5-methylphenyl]methane,bis[4-hydroxy-3-(2-hydroxy-5-methylbenzyl)-5-methylphenyl]methane, andother linear tetranuclear compounds;

[0098]2,6-bis[2,5-dimethyl-3-(2-hydroxy-5-methylbenzyl)-4-hydroxybenzyl]-4-methylphenol,2,4-bis[2-hydroxy-3-(4-hydroxybenzyl)-5-methylbenzyl]-6-cyclohexylphenol,2,4-bis[4-hydroxy-3-(4-hydroxybenzyl)-5-methylbenzyl]-6-cyclohexylphenol,and other linear pentanuclear compounds; and other linear polyphenoliccompounds;

[0099] tris(4-hydroxyphenyl)methane,bis(4-hydroxy-3,5-dimethylphenyl)-4-hydroxyphenylmethane,bis(4-hydroxy-3,5-dimethylphenyl)-3-hydroxyphenylmethane,bis(4-hydroxy-3,5-dimethylphenyl)-2-hydroxyphenylmethane,bis(4-hydroxy-2,5-dimethylphenyl)-4-hydroxyphenylmethane,bis(4-hydroxy-2,5-dimethylphenyl)-3-hydroxyphenylmethane,bis(4-hydroxy-2,5-dimethylphenyl)-2-hydroxyphenylmethane,bis(4-hydroxy-3,5-dimethylphenyl)-3,4-dihydroxyphenylmethane,bis(4-hydroxy-2,5-dimethylphenyl)-3,4-dihydroxyphenylmethane,bis(4-hydroxy-3,5-dimethylphenyl)-2,4-dihydroxyphenylmethane,bis(4-hydroxy-2,5-dimethylphenyl)-2,4-dihydroxyphenylmethane,bis(4-hydroxyphenyl)-3-methoxy-4-hydroxyphenylmethane,bis(3-cyclohexyl-4-hydroxyphenyl)-3-hydroxyphenylmethane,bis(3-cyclohexyl-4-hydroxyphenyl)-2-hydroxyphenylmethane,bis(3-cyclohexyl-4-hydroxyphenyl)-4-hydroxyphenylmethane,bis(3-cyclohexyl-4-hydroxy-6-methylphenyl)-2-hydroxyphenylmethane,bis(3-cyclohexyl-4-hydroxy-6-methylphenyl)-3-hydroxyphenylmethane,bis(3-cyclohexyl-4-hydroxy-6-methylphenyl)-4-hydroxyphenylmethane,bis(3-cyclohexyl-4-hydroxy-6-methylphenyl)-3,4-dihydroxyphenylmethane,bis(3-cyclohexyl-6-hydroxyphenyl)-3-hydroxyphenylmethane,bis(3-cyclohexyl-6-hydroxyphenyl)-4-hydroxyphenylmethane,bis(3-cyclohexyl-6-hydroxyphenyl)-2-hydroxyphenylmethane,bis(3-cyclohexyl-6-hydroxy-4-methylphenyl)-2-hydroxyphenylmethane,bis(3-cyclohexyl-6-hydroxy-4-methylphenyl)-4-hydroxyphenylmethane,bis(3-cyclohexyl-6-hydroxy-4-methylphenyl)-3,4-dihydroxyphenylmethane,bis(4-hydroxy-2,3,5-trimethylphenyl)-2-hydroxyphenylmethane,bis(4-hydroxy-2,3,5-trimethylphenyl)-3-hydroxyphenylmethane,bis(4-hydroxy-2,3,5-trimethylphenyl)-4-hydroxyphenylmethane,bis(4-hydroxy-2,3,5-trimethylphenyl)-3,4-dihydroxyphenylmethane,bis(4-hydroxy-2,3,5-trimethylphenyl)-4-hydroxy-3-methoxyphenylmethane,and other trisphenol polyphenolic compounds; and

[0100]1-[1,1-bis(4-hydroxyphenyl)ethyl]-4-[1-(4-hydroxyphenyl)isopropyl]benzene.

[0101] Among the quinonediazide esters (B) represented by Formula (I),typically preferred compounds for high definition of 0.35 μm or beloware linear esters represented by the following formula:

[0102] wherein R¹ to R⁸, D, a, b and d have the same meanings as definedabove; and m is an integer of from 1 to 3, and branched estersrepresented by the following formula:

[0103] wherein R¹ to R¹³, D, a, b, c and d have the same meanings asdefined above.

[0104] The ingredient (B) for use in the positive photoresistcompositions of the present invention must have at least one1,2-naphthoquinonediazido-5-sulfonyl group in the molecule. By action ofthe 1,2-naphthoquinonediazido-5-sulfonyl group, 1-ethoxyethyl group asan acid-decomposable group in the ingredient (A) can be efficientlydecomposed. In addition, by using the ingredient (B), the positivephotoresist compositions of the present invention can have satisfactorystorage stability, yield less foreign matters formed with time andthereby invite less scum.

[0105] The amount of the ingredient (B) can be selected within the rangeof from about 5% to about 80% by weight, and preferably from about 10%to about 70% by weight, relative to the total weight of the ingredients(A) and (C). If the amount is less than 5% by weight, the resultingphotosensitive composition may fail to form images in exact accordancewith the pattern and may have deteriorated transfer property. Incontrast, if it exceeds 80% by weight, the positive photoresistcomposition may have decreased sensitivity and may fail to yield uniformresist films with high definition.

[0106] Phenolic Compounds (C)

[0107] The ingredient (C) for use in the positive photoresistcomposition of the present invention includes phenolic compoundsrepresented by Formula (III).

[0108] By using the ingredient (C), the positive photoresistcompositions of the present invention yield less scum, exhibit improveddefinition and can thereby yield a patterned resist film with a goodshape in the ultrafine patterning of resist films of 0.35 μm or below.

[0109] Preferred examples of the phenolic compounds (C) represented byFormula (III) includebis(4-hydroxy-2,3,5-trimethylphenyl)-2-hydroxyphenylmethane,bis(4-hydroxy-3,5-dimethylphenyl)-2-hydroxyphenylmethane,bis(4-hydroxy-2,5-dimethylphenyl)-2-hydroxyphenylmethane,bis(4-hydroxy-3,5-dimethylphenyl)-3,4-dihydroxyphenylmethane,1,4-bis[1-(3,5-dimethyl-4-hydroxyphenyl)isopropyl]benzene,1-[1-(4-hydroxyphenyl)isopropyl]-4-[1,1-bis(4-hydroxyphenyl)ethyl]benzene,1-[1-(3-methyl-4-hydroxyphenyl)isopropyl]-4-[1,1-bis(3-methyl-4-hydroxyphenyl)ethyl]benzene,2,6-bis[1-(2,4-dihydroxyphenyl)isopropyl]-4-methylphenol,4,6-bis[1-(4-hydroxyphenyl)isopropyl]resorcin,4,6-bis(3,5-dimethoxy-4-hydroxyphenylmethyl)pyrogallol,4,6-bis(3,5-dimethyl-4-hydroxyphenylmethyl)pyrogallol,2,4-bis(3,5-dimethyl-4-hydroxyphenylmethyl)-6-methylphenol,2,6-bis(2,5-dimethyl-4-hydroxyphenylmethyl)-4-methylphenol,2,6-bis(3-methyl-4,6-dihydroxyphenylmethyl)-4-methylphenol,2,6-bis(2,3,4-trihydroxyphenylmethyl)-4-methylphenol,2,6-bis(2,5-dimethyl-4-hydroxybenzyl)-4-methylphenol, and1,1-bis(4-hydroxyphenyl)cyclohexane.

[0110] Among them, typically preferred are2,6-bis(2,5-dimethyl-4-hydroxybenzyl)-4-methylphenol and1,1-bis(4-hydroxyphenyl)cyclohexane for satisfactory definition andrectangular profile of the resulting resist films.

[0111] The amount of the ingredient (C) can be selected within the rangeof from about 5% to about 50% by weight, and preferably from about 10%to about 40% by weight relative to the weight of the ingredient (A). Ifthe amount is less than 5% by weight, the positive photoresistcomposition may have deteriorated sensitivity. If it exceeds 50% byweight, the positive photoresist composition may invite increased scum.

[0112] Ingredients (D)

[0113] The positive photoresist compositions of the present inventionmay further comprise (D) at least one compound that is capable ofabsorbing light with a wavelength of approximately 365 nm. By using theingredient (D), the positive photoresist compositions of the presentinvention can yield patterned resists having further satisfactoryshapes.

[0114] In the inclined implantation process using a patterned resistthin film about 0.1 to 0.5 μm thick, the patterned resist thin film mayfrequently have a deteriorated shape due to reflected light from thesubstrate. The ingredient (D) is preferably used in the process tomitigate such adverse effects of the reflected light from the substrate.

[0115] Such ingredients (D) for use in the present invention are notspecifically limited, as long as they are miscible with the positivephotoresist compositions and include, for example,2,2,4,4′-tetrahydroxybenzophenone,4-dimethylamino-2′,4′-dihydroxybenzophenone,5-amino-3-methyl-1-phenyl-4-(4-hydroxyphenylazo)pyrazole,4-dimethylamino-4′-hydroxyazobenzene,4-diethylamino-4′-ethoxyazobenzene, 4-diethylaminoazobenzene, andcurcumin. Among them, 2,2,4,4′-tetrahydroxybenzophenone is preferred forits low cost and high halation-preventing capability.

[0116] The amount of the ingredient (D) is preferably controlled so thata resist film formed on a substrate using the positive photoresistcomposition of the present invention has a B parameter of from about 0.2to about 1.0 and more preferably from about 0.3 to about 0.7. The Bparameter represents the absorptivity of the resist film with respect tolight irradiated after exposure of the resist film on the substrate.

[0117] The B parameter can be determined in the following manner.Initially, a sample resist composition is applied to a quartz substrate,is dried (prebaked) and thereby yields a resist film 1.0 μn thick. Next,i-line (365 nm) is applied to the resist film and the transmittance ofthe resist film is determined using an optical parameter measuringsystem (available from Litho Tech Japan Corporation under the trade nameof ABC Analyzer Model 300), and the B parameter is determined bycalculation according to the following equation:

B=(−1/d)×lnT ^(∞)

[0118] wherein d is the thickness of the resist film; and T^(∞)is(transmittance after ultraviolet irradiation)/100.

[0119] While depending on its type, the amount of the ingredient (D), ifany, is preferably selected within the range of from about 0.1% to about5% by weight, and more preferably from about 1% to about 3% by weight,relative to the total weight of the ingredients (A), (B) and (C). If theamount is less than 0.1% by weight, halation from the substrate may notbe prevented sufficiently, and if it exceeds 5% by weight, the resultingcomposition may invite scum formation.

[0120] Amines (E)

[0121] The positive photoresist compositions of the present inventionmay further comprise (E) at least one amine to further improve stabilityof latent image before development.

[0122] Such amines (E) are not specifically limited, as long as they aremiscible with the positive photoresist compositions, and include, forexample, aliphatic amines, aromatic amines, and heterocyclic amines.

[0123] The aliphatic amines include, but are not limited to,methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine,triethylamine, n-propylamine, di-n-propylamine, tri-n-propylamine, andisopropylamine. The aromatic amines include, but are not limited to,benzylamine, aniline, N-methylaniline, N,N-dimethylaniline,o-methylaniline, m-methylaniline, p-methylaniline, N,N-diethylaniline,diphenylamine, and di-p-tolylamine. The heterocyclic amines include, butare not limited to, pyridine, o-methylpyridine, o-ethylpyridine,2,3-dimethylpyridine, 4-ethyl-2-methylpyridine, and3-ethyl-4-methylpyridine.

[0124] Each of these amines can be used alone or in combination as theingredient (E). Among them, the single use of triethylamine is preferredfor further satisfactory patterned resist shape and stability of latentimage before development.

[0125] The amount of the ingredient (E), if any, is preferably fromabout 0.01% to about 2% by weight, and more preferably from about 0.1%to about 1% by weight, relative to the total weight of the ingredients(A), (B), (C) and (D). If the amount is less than 0.01% by weight, thepositive photoresist composition may vary in its sensitivity duringpost-exposure delay (PED). In contrast, if it exceeds 2% by weight,exposure sensitivity may deteriorate.

[0126] Organic Carboxylic Acids (F)

[0127] The positive photoresist compositions of the present inventionmay further comprise (F) at least one organic carboxylic acid for bettershapes of patterned resist films.

[0128] Such organic carboxylic acids (F) are not specifically limited,as long as they are miscible with the positive photoresist compositions,and include, for example, saturated or unsaturated aliphatic carboxylicacids, alicyclic carboxylic acids, hydroxycarboxylic acids,alkoxycarboxylic acids, ketocarboxylic acids, and aromatic carboxylicacids.

[0129] The saturated aliphatic carboxylic acids include, but are notlimited to, formic acid, acetic acid, propionic acid, butyric acid,isobutyric acid, oxalic acid, malonic acid, succinic acid, glutaricacid, adipic acid, and other mono-or poly-carboxylic acids. Theunsaturated aliphatic carboxylic acids include, but are not limited to,acrylic acid, crotonic acid, isocrotonic acid, 3-butenoic acid,methacrylic acid, 4-pentenoic acid, 2-butynoic acid, maleic acid,fumaric acid, and acetylenecarboxylic acid. The alicyclic carboxylicacids include, but are not limited to, 1,1-cyclohexanedicarboxylic acid,1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid,1,4-cyclohexanedicarboxylic acid, and 1,1-cyclohexyldiacetic acid. Thehydroxycarboxylic acids include, for example, hydroxyacetic acid. Thealkoxycarboxylic acids include, for example, methoxyacetic acid andethoxyacetic acid. The ketocarboxylic acids include, for example,pyruvic acid. Examples of the aromatic carboxylic acids arep-hydroxybenzoic acid, o-hydroxybenzoic acid (salicylic acid),2-hydroxy-3-nitrobenzoic acid, 3,5-dinitrobenzoic acid, 2-nitrobenzoicacid, 2,4-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid,2,6-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid,3,5-dihydroxybenzoic acid, 2-vinylbenzoic acid, 4-vinylbenzoic acid,phthalic acid, terephthalic acid, isophthalic acid, and other aromaticcarboxylic acids each having a substituent such as nitro group, carboxylgroup and vinyl group.

[0130] Among these organic carboxylic acids, aromatic carboxylic acidsare preferred since they have appropriate acidity and are nonvolatile,of which salicylic acid is typically preferred since it is highlysoluble in the positive photoresist compositions and can yieldsatisfactory patterned resist films on different types of substrates.

[0131] The amount of the ingredient (F) is, if any, from about 0.01% toabout 2% by weight, and preferably from about 0.1% to about 1% byweight, relative to the total weight of the ingredients (A), (B), (C)and (D). If the amount is less than 0.01% by weight, the positivephotoresist composition may vary in its sensitivity during post-exposuredelay (PED). In contrast, if it exceds 2% by weight, exposuresensitivity may deteriorate

[0132] Additives

[0133] The positive photoresist compositions of the present inventionmay further comprise any of compatible additives such as surfactants forprevention of striation within ranges not adversely affecting theobjects of the invention. Such surfactants include, but are not limitedto, Fluorad FC-430 and FC-431 (trade names, available fromFluorochemical-Sumitomo 3M Co.), EFTOP EF122A, EF122B, EF122C and EF126(trade names, available from Tohkem Products Corporation) and otherfluorine-containing surfactants.

[0134] The positive photoresist compositions of the present inventionare preferably used as a solution prepared by dissolving each of theingredients (A), (B) and (C), and other additional ingredients addedaccording to necessity in an appropriate solvent. Such solvents includethose conventionally used in positive photoresist compositions, such asacetone, methyl ethyl ketone, cyclohexanone, methyl isoamyl ketone,2-heptanone, and other ketones; ethylene glycol, propylene glycol,diethylene glycol, ethylene glycol monoacetate, propylene glycolmonoacetate, diethylene glycol monoacetate, and monomethyl ethers,monoethyl ethers, monopropyl ethers, monobutyl ethers and monophenylethers thereof, and other polyhydric alcohols and derivatives thereof;dioxane and other cyclic ethers; and ethyl lactate, methyl acetate,ethyl acetate, butyl acetate, methyl pyruvate, ethyl pyruvate, methylmethoxypropionate, ethyl ethoxypropionate, and other esters. Each ofthese solvents can be used alone or in combination. Of these solvents,preferred are acetone, methyl ethyl ketone, cyclohexanone, methylisoamyl ketone, 2-heptanone, and other ketones; and ethyl lactate,methyl acetate, ethyl acetate, butyl acetate, methyl pyruvate, ethylpyruvate, methyl methoxypropionate, ethyl ethoxypropionate, and otheresters.

[0135] Practically, the positive photoresist compositions of the presentinvention may preferably be used, for example, in the following manner.Each of the ingredients (A), (B) and (C) and other ingredients addedaccording to necessity is dissolved in an appropriate solvent asmentioned above to yield a coating solution; the coating solution isthen applied, using a spinner or the like, onto a substrate such as asilicon wafer, and is then dried to form a resist film (photosensitivelayer) about 0.1 to 0.5 μm thick; next, the resist film is selectivelyexposed to light through a desired mask pattern using a light sourceemitting light with a wavelength of approximately 365 nm, such as alow-pressure mercury lamp, high-pressure mercury lamp, andultrahigh-pressure mercury lamp; the exposed resist film is subjected topost-exposure baking (PEB) at about 100° C. to about 120° C.; and theexposed portions of the film are then dissolved and removed by dippingthe substrate in a developer solution, for example, an alkaline aqueoussolution such as a 1% to 10% by weight tetramethylammonium hydroxide(TMAH) aqueous solution, thus forming an image being in exact accordancewith the mask pattern. The resist film is then subjected to post-bakingat about 90° C. to about 110° C. and thereby yields a patterned resistthin film for use in an inclined implantation process.

[0136] The patterned resist thin film invites less scum, is excellent inthermal resistance and has a good shape even when it is very thin ofabout 0.1 to 0.5 μm. Accordingly, the patterned resist thin film can beadvantageously used as a patterned resist mask in ion implantationprocesses such as an inclined implantation process.

EXAMPLES

[0137] The present invention will be illustrated in further detail withreference to several examples and comparative examples below, which arenot intended to limit the scope of the invention.

[0138] The physical properties of the resulting positive photoresistcompositions were determined by the following methods.

[0139] (1) Sensitivity

[0140] A sample was applied onto a silicon wafer using a spinner and wasdried on a hot plate at 90° C. for 90 seconds to form a resist film 0.32μm thick; the resist film was then irradiated with light for anincreasing period from 0.1 second at intervals of 0.01 second using areducing-type projection aligner NSR-2005i10D (available from NikonCorporation, Japan; NA=0.57). The film was then post-exposure baked(PEB) at 110° C. for 90 seconds; was subjected to development in a 2.38%by weight tetramethylammonium hydroxide (TMAH) aqueous solution at 23°C. for 60 seconds, was rinsed with water for 30 seconds, and was dried.In this procedure, the sensitivity was defined as the exposure timeperiod (Eth) in milliseconds (ms) at the time when the thickness ofexposed portions became zero.

[0141] (2) Definition

[0142] The definition was defined as the critical definition at anexposure to reproduce a 0.5-μm mask pattern with a line-and-space (L&S)width of 1:1.

[0143] (3) Profile

[0144] A 0.5-μm wide resist pattern was subjected to scanning electronmicrographic (SEM) observation on profile (sectional shape). The profilewas rated based on the SEM observation according to the followingcriteria:

[0145] Excellent: Rectangular profile

[0146] Good: Almost rectangular profile with some T-top shape orintrusion at the interface of the substrate

[0147] Poor: No isolated pattern obtained

[0148] (4) Scum Formation

[0149] A sample was applied onto a silicon wafer using a spinner and wasdried on a hot plate at 90° C. for 90 seconds to form a resist film 0.32μm thick. The resist film was then irradiated with light at an exposureof Eop (the exposure time period to reproduce a 0.35-μm pattern withline-and-space (L&S) of 1:1) as a standard exposure using areducing-type projection aligner NSR-2005i10D (available from NikonCorporation, Japan; NA=0.57). The resist film was then post-exposurebaked (PEB) at 110° C. for 90 seconds, was subjected to development in a2.38% by weight TMAH aqueous solution at 23° C. for 60 seconds, wasrinsed with water for 30 seconds, and was dried. The resist film wasthen post-based at 100° C. for 60 seconds and thereby yielded apatterned resist. The whole surface of the substrate having thepatterned resist was subjected to an SEM observation. Based on the SEMobservation, the scum formation was rated according to the followingcriteria:

[0150] Good: Little scum observed

[0151] Poor: A large amount of scum observed

[0152] (5-1) Stability of Latent Image Before Development: Post-CoatingDelay PCD

[0153] A sample was applied onto a silicon wafer using a spinner and wasdried on a hot plate at 90° C. for 90 seconds to form a resist film 0.32μm thick. The resist film was stored for 8 hours in a room under regularconditions for use of i-line resist without deamination by means ofchemical filter. The resist film was then irradiated with light for anincreasing period from 0.1 second at intervals of 0.01 second using areducing-type projection aligner NSR-2005i10D (available from NikonCorporation, Japan; NA=0.57). The film was then post-exposure baked(PEB) at 110° C. for 90 sec.; was subjected to development in a 2.38% byweight TMAH aqueous solution at 23° C. for 60 seconds, was rinsed withwater for 30 seconds, and was dried. In this procedure, the exposuretime period (Eth1) at which the thickness of exposed portions becamezero was determined, and the post-coating delay (PCD) was determined bycalculation according to the following equation:

PCD=(|Eth1−Eth|/Eth)×100(%)

[0154] The lower PCD is, the higher the stability of latent image beforedevelopment is.

[0155] (5-2) Stability of Latent Image Before Development: Post-ExposureDelay PED

[0156] A sample was applied onto a silicon wafer using a spinner and wasdried on a hot plate at 90° C. for 90 seconds to form a resist film 0.32μm thick. The resist film was then irradiated with light for anincreasing period from 0.1 second at intervals of 0.01 second using areducing-type projection aligner NSR-2005i10D (available from NikonCorporation, Japan; NA=0.57). The exposed resist film was stored for 8hours in a room under regular conditions for use of i-line resistwithout deamination by means of chemical filter. The film waspost-exposure baked (PEB) at 110° C. for 90 seconds, was subjected todevelopment in a 2.38% by weight TMAH aqueous solution at 23° C. for 60seconds, was rinsed with water for 30 seconds, and was dried. In thisprocedure, the exposure time period (Eth2) at which the thickness ofexposed portions became zero was determined, and the post-exposure delay(PED) was determined by calculation according to the following equation:

PED=(|Eth2−Eth|/Eth)×100(%)

[0157] The lower PED is, the higher the stability of latent image beforedevelopment is.

Preparation Example 1

[0158] Preparation of Novolak Resin A1

[0159] A total of 108 g (1 mol) of m-cresol, 1 g (0.005 mol) ofp-toluenesulfonic acid hydrate, and 162 g of γ-butyrolactone were placedin a 1-liter separable four-neck flask, and the flask was equipped witha dropping funnel, a condenser tube, a thermometer and a mechanicalstirrer. The mixture was stirred, and the flask was heated in an oilbath stirred with a magnetic stirrer. When the temperature of thereaction system reached 100° C., 64.8 g (0.8 mol) of 37% by weightformaldehyde aqueous solution was gradually added dropwise from thedropping funnel to the reaction system over 20 minutes. After thecompletion of addition, the reaction system was allowed to react for 4hours while maintaining its temperature at 100° C. After the completionof reaction, the reaction system was cooled to room temperature and wasneutralized with 0.6 g (0.006 mol) of triethylamine. The resultingmixture was diluted with 400 g of 2-heptanone, was placed in a 3-literseparatory funnel, was washed with three portions of 1 liter of purewater; the organic layer was extracted, was concentrated using anevaporator and thereby yielded a solution of a novolak resin(unprotected novolak resin). The obtained unprotected novolak resin hada weight average molecular weight Mw of 2600, a molecular weightdistribution Mw/Mn of 3.96 and a dissolution time Dt(2.38) of 4.0seconds.

[0160] The dissolution time Dt(2.38) was determined in the followingmanner. The novolak resin solution was applied to a substrate, was driedat 110° C. for 90 seconds and thereby yielded a resist film 1 μm thick.The resist film was then dissolved in 2.38% by weight TMAH aqueoussolution at 23° C. In this procedure, the dissolution time Dt(2.38) wasdefined as the time for the resist film to completely dissolve in theTMAH aqueous solution.

[0161] The above-prepared unprotected novolak resin solution (solidcontent: 120 g, equivalent to 1 mole hydroxyl group) was placed in a1-liter egg plant type flask, was diluted with 1,4-dioxane to aconcentration of 15% by weight, was treated with an ion exchange resinand was concentrated using an evaporator to a concentration of 20% byweight. The mixture was cooled to room temperature; was treated with36.0 g (0.5 mol) of 1-ethoxyethene, corresponding to 50% of moleequivalent of hydroxyl groups in the unprotected novolak resin, and with0.024 g (0.125 mmol) of p-toluenesulfonic acid at room temperature for 1hour with stirring. The mixture was then neutralized with 0.025 g (0.25mmol) of triethylamine, was treated with an ion exchange resin, wasconcentrated using an evaporator and thereby yielded a solution of anovolak resin A1 having a 1-ethoxyethyl group substituting for 50% bymole of hydrogen atoms of phenolic hydroxyl groups. The novolak resin A1had a dissolution time Dt(5.0) of more than 300 seconds.

[0162] The dissolution time Dt(5.0) was determined in the followingmanner. The novolak resin solution was applied to a substrate, was driedat 110° C. for 90 seconds and thereby yielded a resist film 1 μm thick.The resist film was then dissolved in 5.0% by weight TMAH aqueoussolution at 23° C. In this procedure, the dissolution time Dt(5.0) wasdefined as the time for the resist film to completely dissolve in theTMAH aqueous solution.

Preparation Example 2

[0163] Preparation of Novolak Resin A2

[0164] A total of 86.4 g (0.8 mol) of m-cresol, 24.4 g (0.2 mol) of3,4-xylenol, 1 g (0.005 mol) of p-toluenesulfonic acid hydrate, and 162g of γ-butyrolactone were placed in a 1-liter separable four-neck flask,and the flask was equipped with a dropping funnel, a condenser tube, athermometer and a mechanical stirrer. The mixture was stirred, and theflask was heated in an oil bath stirred with a magnetic stirrer. Whenthe temperature of the reaction system reached 100° C., 66.9 g (0.83mol) of 37% by weight formaldehyde aqueous solution was gradually addeddropwise from the dropping funnel to the reaction system over 20minutes. After the completion of addition, the reaction system wasallowed to react for 4 hours while maintaining its temperature at 100°C. After the completion of reaction, the reaction system was cooled toroom temperature and was neutralized with 0.6 g (0.006 mol) oftriethylamine. The resulting mixture was diluted with 400 g of2-heptanone, was placed in a 3-liter separatory funnel, was washed withthree portions of 1 liter of pure water; the organic layer wasextracted, was concentrated using an evaporator and thereby yielded asolution of an unprotected novolak resin. The obtained unprotectednovolak resin had a weight average molecular weight Mw of 2900, amolecular weight distribution Mw/Mn of 3.89 and a dissolution timeDt(2.38) of 3.0 seconds.

[0165] The above-prepared unprotected novolak resin solution (solidcontent: 120 g, equivalent to 1 mole hydroxyl group) was placed in a1-liter egg plant type flask, was diluted with 1,4-dioxane to aconcentration of 15% by weight, was treated with an ion exchange resinand was concentrated using an evaporator to a concentration of 20% byweight. The mixture was cooled to room temperature; was treated with36.0 g (0.5 mol) of 1-ethoxyethene, corresponding to 50% of moleequivalent of hydroxyl groups in the novolak resin, and with 0.024 g(0.125 mmol) of p-toluenesulfonic acid at room temperature for 1 hourwith stirring. The mixture was then neutralized with 0.025 g (0.25 mmol)of triethylamine, was treated with an ion exchange resin, wasconcentrated using an evaporator and thereby yielded a solution of anovolak resin A2 having a 1-ethoxyethyl group substituting for 50% bymole of hydrogen atoms of phenolic hydroxyl groups. The novolak resin A2had a dissolution time Dt(5.0) of more than 300 seconds.

Preparation Example 3

[0166] Preparation of Novolak Resin A3

[0167] The unprotected novolak resin solution (solid content: 120 g,equivalent to 1 mole hydroxyl group) prepared in Preparation Example 1was placed in a 1-liter egg plant type flask, was diluted with1,4-dioxane to a concentration of 15% by weight, was treated with an ionexchange resin and was concentrated using an evaporator to aconcentration of 20% by weight. The mixture was cooled to roomtemperature; was treated with 50.4 g (0.7 mol) of 1-ethoxyethene,corresponding to 70% of mole equivalent of hydroxyl groups in thenovolak resin, and with 0.033 g (0.17 mmol) of p-toluenesulfonic acid atroom temperature for 1 hour with stirring. The mixture was thenneutralized with 0.035 g (0.35 mmol) of triethylamine, was treated withan ion exchange resin, was concentrated using an evaporator and therebyyielded a solution of a novolak resin A3 having 1-ethoxyethyl groupssubstituting for 70% by mole of hydrogen atoms of phenolic hydroxylgroups. The novolak resin A3 had a dissolution time Dt(5.0) of more than300 seconds.

Comparative Preparation Example 1

[0168] Preparation of Novolak Resin A4

[0169] The unprotected novolak resin solution (solid content: 120 g,equivalent to 1 mole hydroxyl group) prepared in Preparation Example 1was placed in a 1-liter egg plant type flask, was diluted with1,4-dioxane to a concentration of 15% by weight, was treated with an ionexchange resin and was concentrated using an evaporator to aconcentration of 20% by weight. The mixture was cooled to roomtemperature; was treated with 109 g (0.5 mol) of di-tert-butyldicarbonate, corresponding to 50% of mole equivalent of hydroxyl groupsin the unprotected novolak resin, and with 68.2 g (0.675 mmol) oftriethylamine at 40° C. for 1 hour with stirring. The mixture was thenneutralized with 6 liters of acetic acid aqueous solution containing 50g (0.83 mol) of acetic acid in pure water, and the precipitated resinwas separated by filtration.

[0170] The resin was dissolved in dioxane, was subjected to treatmentwith an ion exchange resin, was concentrated using an evaporator andthereby yielded a solution of a novolak resin A4 having atert-butoxycarbonyl group substituting for 50% by mole of hydrogen atomsof phenolic hydroxyl groups. The novolak resin A4 had a dissolution timeDt(5.0) of more than 300 seconds.

Comparative Preparation Example 2

[0171] Preparation of Novolak Resin A5

[0172] A total of 108 g (1 mol) of o-cresol, 1 g (0.005 mol) ofp-toluenesulfonic acid hydrate, and 162 g of γ-butyrolactone were placedin a 1-liter separable four-neck flask, and the flask was equipped witha dropping funnel, a condenser tube, a thermometer and a mechanicalstirrer. The mixture was stirred, and the flask was heated in an oilbath stirred with a magnetic stirrer. When the temperature of thereaction system reached 100° C., 81.1 g (1.0 mol) of 37% by weightformaldehyde aqueous solution was gradually added dropwise from thedropping funnel to the reaction system over 20 minutes. After thecompletion of addition, the reaction system was allowed to react for 8hours while maintaining its temperature at 100° C. After the completionof reaction, the reaction system was cooled to room temperature and wasneutralized with 0.6 g (0.006 mol) of triethylamine. The resultingmixture was diluted with 400 g of 2-heptanone, was placed in a 3-literseparatory funnel, was washed with three portions of 1 liter of purewater; the organic layer was extracted, was concentrated using anevaporator and thereby yielded a solution of a novolak resin(unprotected novolak resin). The obtained unprotected novolak resin hada weight average molecular weight Mw of 2600, a molecular weightdistribution Mw/Mn of 2.09 and a dissolution time Dt(2.38) of 3.0seconds.

[0173] The above-prepared unprotected novolak resin solution (solidcontent: 120 g, equivalent to 1 mole hydroxyl group) was placed in a1-liter egg plant type flask, was diluted with 1,4-dioxane to aconcentration of 15% by weight, was treated with an ion exchange resinand was concentrated using an evaporator to a concentration of 20% byweight. The mixture was cooled to room temperature; was treated with36.0 g (0.5 mol) of 1-ethoxyethene, corresponding to 50% of moleequivalent of hydroxyl groups in the novolak resin, and with 0.024 g(0.125 mmol) of p-toluenesulfonic acid at room temperature for 1 hourwith stirring. The mixture was then neutralized with 0.025 g (0.25 mmol)of triethylamine, was treated with an ion exchange resin, wasconcentrated using an evaporator and thereby yielded a solution of anovolak resin A5 having 1-ethoxyethyl groups substituting for 50% bymole of hydrogen atoms of phenolic hydroxyl groups. The novolak resin A5had a dissolution time Dt(5.0) of more than 300 seconds.

Comparative Preparation Example 3

[0174] Preparation of Novolak Resin A6

[0175] A total of 75.6 g (0.7 mol) of o-cresol, 32.4 g (0.3 mol) ofp-cresol, 1 g (0.005 mol) of p-toluenesulfonic acid hydrate, and 162 gof γ-butyrolactone were placed in a 1-liter separable four-neck flask,and the flask was equipped with a dropping funnel, a condenser tube, athermometer and a mechanical stirrer. The mixture was stirred, and theflask was heated in an oil bath stirred with a magnetic stirrer. Whenthe temperature of the reaction system reached 100° C., 101.4 g (1.25mol) of 37% by weight formaldehyde aqueous solution was gradually addeddropwise from the dropping funnel to the reaction system over 20minutes. After the completion of addition, the reaction system wasallowed to react for 16 hours while maintaining its temperature at 100°C. After the completion of reaction, the reaction system was cooled toroom temperature and was neutralized with 0.6 g (0.006 mol) oftriethylamine. The resulting mixture was diluted with 400 g of2-heptanone, was placed in a 3-liter separatory funnel, was washed withthree portions of 1 liter of pure water; the organic layer wasextracted, was concentrated using an evaporator and thereby yielded asolution of an unprotected novolak resin. The obtained unprotectednovolak resin had a weight average molecular weight Mw of 1900, amolecular weight distribution Mw/Mn of 2.5 and a dissolution timeDt(2.38) of 3.0 seconds.

[0176] The above-prepared unprotected novolak resin solution (solidcontent: 120 g, equivalent to 1 mole hydroxyl group) was placed in a1-liter egg plant type flask, was diluted with 1,4-dioxane to aconcentration of 15% by weight, was treated with an ion exchange resinand was concentrated using an evaporator to a concentration of 20% byweight. The mixture was cooled to room temperature; was treated with36.0 g (0.5 mol) of 1-ethoxyethene, corresponding to 50% of moleequivalent of hydroxyl groups in the novolak resin, and with 0.024 g(0.125 mmol) of p-toluenesulfonic acid at room temperature for 1 hourwith stirring. The mixture was then neutralized with 0.025 g (0.25 mmol)of triethylamine, was treated with an ion exchange resin, wasconcentrated using an evaporator and thereby yielded a solution of anovolak resin A6 having a 1-ethoxyethyl group substituting for 50% bymole of hydrogen atoms of phenolic hydroxyl groups. The novolak resin A6had a dissolution time Dt(5.0) of more than 300 seconds.

Comparative Preparation Example 4

[0177] Preparation of Polyhydroxystyrene S1

[0178] A total of 120 g (1 mol) of 4-hydroxystyrene was added totetrahydrofuran (THF) to a concentration of 20% by weight in a 1-literthree-neck flask equipped with a condenser tube; the mixture was stirredwith a magnetic stirrer and thereby yielded a solution; the solution wassubjected to radical polymerization at 75° C. under reflux usingazobisisobutyronitrile (AIBN) as a polymerization initiator and therebyyielded a solution of a polyhydroxystyrene. The preparedpolyhydroxystyrene had a weight average molecular weight Mw of 12700, amolecular weight distribution Mw/Mn of 2.7, and a dissolution timeDt(2.38) of 3.0 seconds.

[0179] The above-prepared polyhydroxystyrene solution (solid content:120 g, equivalent to 1 mole hydroxyl group) was placed in a 1-liter eggplant type flask, was diluted with 1,4-dioxane to a concentration of 15%by weight, was treated with an ion exchange resin and was concentratedusing an evaporator to a concentration of 20% by weight. The mixture wascooled to room temperature, was treated with 36.0 g (0.5 mol) of1-ethoxyethene, corresponding to 50% of mole equivalent of hydroxylgroups in the polyhydroxystyrene, and with 0.024 g (0.125 mmol) ofp-toluenesulfonic acid at room temperature for 1 hour with stirring. Themixture was then neutralized with 0.025 g (0.25 mmol) of triethylamine,was treated with an ion exchange resin, was concentrated using anevaporator and thereby yielded a solution of a polyhydroxystyrene S1having 1-ethoxyethyl groups substituting for 50% by mole of hydrogenatoms of phenolic hydroxyl groups. The polyhydroxystyrene S1 had adissolution time Dt(5.0) of 35 seconds.

Examples 1 to 3 and Comparative Examples 1 to 4

[0180] Ingredient (A): Novolak resins A1 to A6 and polyhydroxystyrene S1prepared in Preparation Examples 1 to 3 and Comparative PreparationExamples 1 to 4

[0181] Ingredient (B): A quinonediazide ester prepared from 1 mole of aphenolic compound represented by the following formula and 2 moles of1,2-naphthoquinonediazido-5-sulfonyl chloride

[0182] Ingredient (C): 1,1-Bis(4-hydroxyphenyl)cyclohexane

[0183] Ingredient (D): 2,2′,4,4′-Tetrahydroxybenzophenone

[0184] Ingredient (E): Triethylamine

[0185] Ingredient (F): Salicylic acid

[0186] In 1068 parts by weight of 2-heptanone were dissolved 100 partsby weight of the ingredient (A), 66.5 parts by weight of the ingredient(B), 33 parts by weight of the ingredient (C), 4 parts by weight of theingredient (D), 0.6 part by weight of the ingredient (E), and 0.6 partby weight of the ingredient (F); the resulting solution was filtratedusing a 0.2-μm membrane filter and thereby yielded a series of positivephotoresist compositions.

[0187] The physical properties (1) through (5-2) of the preparedpositive photoresist compositions were determined, and the results areshown in Table 1.

Example 4

[0188] A positive photoresist composition was prepared by the process ofExample 1, except using, as the ingredient (B), a 2:1 by weight mixtureof (b-1) a quinonediazide ester prepared from 1 mole of a phenoliccompound represented by the following formula:

[0189] and 2 moles of 1,2-naphthoquinonediazido-5-sulfonyl chloride, and(b-2) a quinonediazide ester prepared from 1 mole of a phenolic compoundrepresented by the following formula:

[0190] and 3 moles of 1,2-naphthoquinonediazido-5-sulfonyl chloride. Thephysical properties (1) through (5-2) of the prepared positivephotoresist composition were determined, and the results are shown inTable 1.

Example 5

[0191] A positive photoresist composition was prepared by the procedureof Example 4, except using, as the ingredient (C), a 2:1 by weightmixture of 1,1-bis(4-hydroxyphenyl)cyclohexane and2,6-bis(2,5-dimethyl-4-hydroxybenzyl)-4-methylphenol. The physicalproperties (1) through (5-2) of the prepared positive photoresistcomposition were determined, and the results are shown in Table 1.

Comparative Example 5

[0192] A positive photoresist composition was prepared by the procedureof Example 1, except that the ingredient (C) was not used. The physicalproperties (1) through (5-2) of the prepared positive photoresistcomposition were determined, and the results are shown in Table 1. TABLE1 Stability of Ingredient Sensitivity Definition latent image (A) (ms)(μm) Profile Scum PCD PED Ex. 1 A1 150 0.28 Good Good 0% 0% Ex. 2 A2 2000.28 Good Good 0% 0% Ex. 3 A3 120 0.30 Good Good 0% 0% Ex. 4 A1 180 0.28Excellent Good 0% 0% Ex. 5 A1 180 0.28 Excellent Good 0% 0% Com. Ex. 1A4 — not Poor — — — resolved Com. Ex. 2 A5 140 0.35 Good Poor 0% 0% Com.Ex. 3 A6 200 0.32 Good Poor 0% 0% Com. Ex. 4 S1 100 0.32 Good Good 3%30% Com. Ex. 5 A1 500 not Poor Good 0% 0% resolved

[0193] While the present invention has been described with reference towhat are presently considered to be the preferred embodiments, it is tobe understood that the invention is not limited to the disclosedembodiments. On the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the sprit andscope of the appended claims. The scope of the following claims is to beaccorded the broadest interpretation so as to encompass all suchmodifications and equivalent structures and functions.

What is claimed is:
 1. A positive photoresist composition comprising:(A) a novolak resin containing equal to or more than 20% by mole of am-cresol constitutional repeating unit in total phenolic constitutionalrepeating units and having 1-ethoxyethyl groups substituting for part ofhydrogen atoms of phenolic hydroxyl groups; (B) a quinonediazide esterrepresented by following Formula (I):

wherein each of R¹, R² R³, R⁴, R⁵, R⁶, R⁷, and R⁸ is independently ahydrogen atom, a halogen atom, an alkyl group containing 1 to 6 carbonatoms, an alkoxy group containing 1 to 6 carbon atoms, or a cycloalkylgroup; each of R⁹, R¹⁰, and R¹¹ is independently a hydrogen atom or analkyl group containing 1 to 6 carbon atoms; Q is a hydrogen atom or analkyl group containing 1 to 6 carbon atoms, or Q is combined with R⁹ toform a cycloalkyl group containing 3 to 6 carbon members or a residuerepresented by following Formula (II):

wherein each of R¹² and R¹³ is independently a hydrogen atom, a halogenatom, an alkyl group containing 1 to 6 carbon atoms, an alkoxy groupcontaining 1 to 6 carbon atoms, or a cycloalkyl group; and c is aninteger of from 1 to 3; each of Ds is independently a hydrogen atom or a1,2-naphthoquinonediazido-5-sulfonyl group, where at least one of Ds isa 1,2-naphthoquinonediazido-5-sulfonyl group; each of a and b isindependently an integer of from 1 to 3; d is an integer of from 0 to 3;and n is an integer of from 0 to 3; and (C) a phenolic compoundrepresented by following Formula (III):

wherein each of R¹, R², R³, R⁴, R⁵, R⁶, R⁷, and R⁸ is independently ahydrogen atom, a halogen atom, an alkyl group containing 1 to 6 carbonatoms, an alkoxy group containing 1 to 6 carbon atoms, or a cycloalkylgroup; each of R⁹, R¹⁰, and R¹¹ is independently a hydrogen atom or analkyl group containing 1 to 6 carbon atoms; Q is a hydrogen atom or analkyl group containing 1 to 6 carbon atoms, or Q is combined with R⁹ toform a cycloalkyl group containing 3 to 6 carbon members or a residuerepresented by following Formula (IV):

wherein each of R¹² and R¹³ is independently a hydrogen atom, a halogenatom, an alkyl group containing 1 to 6 carbon atoms, an alkoxy groupcontaining 1 to 6 carbon atoms, or a cycloalkyl group; and c is aninteger of from 1 to 3; each of a and b is independently an integer offrom 1 to 3; d is an integer of from 0 to 3; and n is an integer of from0 to
 3. 2. The positive photoresist composition according to claim 1,further comprising (D) at least one compound capable of absorbing lightwith a wavelength of approximately 365 nm.
 3. The positive photoresistcomposition according to one of claims 1 and 2, further comprising (E)at least one amine.
 4. The positive photoresist composition according toany one of claims 1 to 3, further comprising (F) at least one organiccarboxylic acid.
 5. The positive photoresist composition according toclaim 1, wherein the 1-ethoxyethyl group substitutes for 30% to 70% bymole of hydrogen atoms of phenolic hydroxyl groups of the novolak resin(A).
 6. The positive photoresist composition according to any one ofclaims 1 to 5, wherein a resist film prepared from the positivephotoresist composition has a B parameter of from 0.2 to 1.0.
 7. Amethod of patterning a resist thin film for use in an inclinedimplantation process, the method comprising the steps of: (1) applying asolution of the positive photoresist composition of any one of claims 1to 6 to a substrate and drying the applied solution to thereby form aresist film having a thickness of from 0.1 to 0.5 μm; (2) selectivelyexposing the resist film to light through a mask; (3) subjecting theexposed resist film to post-exposure baking; (4) developing theresulting resist film with an aqueous alkaline solution to therebydissolve and remove exposed portions of the resist film; and (5)post-baking the resulting film.